Sentient creatures supposedly artificially created by Deus to create or modify other living creatures.
Appearance
The abilities allow them to change their own bodies and so can greatly vary in looks, often they choose to stick to one form though, but the form mostly would be very individual depending on the Engineer.
Abilities
They have abilities to change any life that is based on DNA.
The Engineers have to have extensive knowledge in biology and medicine to perform their flesh-changing actions. At some point of experience the actions become more of an intuitive kind taking no much of a cognitive effort.
They can change DNA of body cells, create stem cells of any kind, control the vegetative systems including metabolism of anyone whos body they can get in touch with allowing them them to heal or change any living creature or even create new ones from scratch.